The present invention relates to laboratory glassware and more specifically to a dual-filtering apparatus using at least one fritted disc and a pre-filter to filter out solid particles, precipitate, or residue from a gaseous substance.
Laboratory glassware generally refers to a variety of devices, traditionally made of glass, suitable for scientific experiments and other work in science, particularly for use in chemistry and biology laboratories. Glass is often preferred in such environments because it is relatively inert, transparent, heat-resistant, and relatively easy to configure as needed for a particular experiment or application. Borosilicate laboratory glass-often sold under the trade name “Pyrex,” is commonly utilized as its chemical inertness, transparency, and resistance to thermal stress make it the ideal material for most wet chemistry reactions.
Other types of glass are known in this art. For example, in some applications quartz glass is used: it can withstand high temperatures and offers transparency in certain parts of the electromagnetic spectrum. In other applications, especially some storage bottles, darkened brown or amber (actinic) glass is used to keep out much of the UV and IR radiation so that the effect of light on the contents is minimized. Heavy-wall glass is used for pressure reactors.
One particularly specialized use of glass in the laboratory includes glass as a filter device. Such a glass filter, termed fritted glass, is finely porous glass mass through which gas or liquid may pass. It is made by sintering together glass particles into a solid but porous body. This porous glass body can be called a frit. Applications in laboratory glassware include use in fritted glass filter items, scrubbers, or spargers. Other laboratory applications of fritted glass include packing in chromatography columns and resin beds for special chemical synthesis.
In a fritted glass filter, a disc or pane of fritted glass is used to filter out solid particles, precipitate, or residue from a fluid (or gas), which passes through the pores in the fritted glass. In the case of a gas, a pressure difference is often required to either push or draw the gas through the fritted filter. The liquid or gas passes through the fritted filter, but any solid (larger than the porosity of the frit) will be prevented from flowing through the frit.
Fritted glass is manufactured from individual bead or particles of glass fused, or sintered, into a solid, but porous glass body. Fritted discs are made by heating glass particles or fibers at a high enough temperature that they fuse together sufficiently that they become a relatively strong mass with a desired porosity. For example, a borosilicate glass frit can be made from particulate glass or from short pieces of fiber.
The porosity of a frit is related to the mesh range of the glass beads (particles) or fibers. The mesh range of glass beads or packing determines a nominal particle size: For example, a 200-400 mesh corresponds to 37-74 μm, and are sometimes called out as 40 μm. This means that a frit with a pore size of 16-40 μm will not clog when used to support a nominal 40 μm packing. Commonly, a frit may be classified as a medium porosity frit having 10-15-μm porosity, a coarse porosity frit having a 40-60 μm porosity, or an extra-coarse porosity frit having a 170-220 μm porosity.
A single fritted filter is a common part of laboratory glassware and such items as fritted glass funnels and fritted glass crucibles are generally known and available in this art. Such single-fritted-filter device include a laboratory scale sparger (also known as gas diffusing stones or diffusors), a scrubber, and a gas-washing bottle (or Drechsel bottle). Such devices include a fritted glass piece fused to the tip of a gas-inlet tube. This fritted glass tip is placed inside the vessel with liquid inside during use such that the fritted tip is submerged in the liquid. To maximize surface area contact of the gas to the liquid, a gas stream is slowly blown into the vessel through the fritted glass tip so that it breaks up the gas into many tiny bubbles. The purpose of sparging is to saturate the enclosed liquid with the gas, often to displace another gaseous component. The purpose of a scrubber or gas-washing bottle is to scrub the gas such that the liquid absorbs one (or more) of the gaseous components to remove it from the gas stream, effectively purifying the gas stream.
One exemplary single fritted filter laboratory glassware, described by Johnstone in U.S. patent application Ser. No. 248,739 issued on 25 Oct. 1949, includes two chambers, one being placed within the other so that there is an annular space between the two chambers. A single fritted disc locates in the inner chamber to scrub a gas as it enters the chamber. Another example of single fritted disc filter includes the device of U.S. Pat. No. 4,363,639 to Gladon issued on 14 Dec. 1982.
Despite the benefits of a single stage (one fritted disc) filtration device, there remains a need for an apparatus having two fritted discs, or at least one fritted disk in line with a pre-filter, or preferably a serviceable, removable pre-filter which may be a fritted glass disc or other incombustible porous medium in line with the main fritted filter disc. A dual filtration device better enables scrubbing gas from a direct combustion process, which results in solid combustion byproducts, either burned to ash or incompletely so. Separating the solids from the gas prior to filtration has two primary benefits: (1) Dry recovery of combusted or heated materials, which allows for further analysis of post process materials; and (B) Dry recovery, which prevents contamination of main filter surface by particulates and resins.